Incorporating Migration Into an Age-Structured Population Model With Variable Mortality Rate

The Potential Effects of Policy Changes on Drug Markets in the UK and Australia: Estimates from a Survey of Drug Users

Extinction and periodic oscillations in an age-structured population model in a patchy environment

Background:The geographic range of the tick Amblyomma americanum, a vector of diseases of public health significance such as ehrlichiosis, has expanded from the southeast of the United States northward during the 20th century. Recently, populations of this tick have been reported to be present close to the Canadian border in Michigan and New York states, but established populations are not known in Canada. Previous research suggests that changing temperature patterns with climate change may influence tick life cycles and permit northward range expansion of ticks in the northern hemisphere.Objectives:We aimed to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick’s range and to investigate the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades.Methods:A simulation model of the tick A. americanum was used, via simulations using climate data from meteorological stations in the United States and Canada, to estimate minimal temperature conditions for survival of A. americanum populations at the northern edge of the tick’s range.Results:The predicted geographic scope of temperature suitability [ annual cumulative degree days (DD) ] included most of the central and eastern U.S. states east of longitude 110°W, which is consistent with current surveillance data for the presence of the tick in this region, as well as parts of southern Quebec and Ontario in Canada. Regional climate model output raises the possibility of northward range expansion into all provinces of Canada from Alberta to Newfoundland and Labrador during the coming decades, with the greatest northward range expansion (up to by the year 2100) occurring under the greenhouse gas (GHG) emissions of Representative Concentration Pathway (RCP) 8.5. Predicted northward range expansion was reduced by approximately half under the reduced GHG emissions of RCP4.5.Discussion:Our results raise the possibility of range expansion of A. americanum into northern U.S. states and southern Canada in the coming decades, and conclude that surveillance for this tick, and the diseases it transmits, would be prudent. https://doi.org/10.1289/EHP5668

Auditing the effect of experience and change on home parenteral nutrition related complications

Approximating the survival probability in finite life-span population models

Mothers of pre‐school children represent one part of the population that might be able to increase its labour supply. We discuss the effects of family policy changes that encourage the labour supply of these mothers, such as childcare fee reductions and increased availability of centre‐based care. The effects of policy changes are described by using a joint labour supply and childcare choice decision model. Detailed empirical results are provided with respect to mothers' labour supply, families' childcare choices, public expenditures, and distributions of income and money metric utility.

Timber supply is a primary object of economic modeling in forestry, especially in the context of policy evaluation. Policy changes have two potential effects on timber supply. First, they may change the relationship between the quantity of timber harvested and its determinants. Secondly, they may alter the values of the factors that influence timber supply. A standard approach for policy evaluation is to estimate the supply function from observed harvest behavior, and then use the obtained supply function to simulate the effects of policy changes. A limitation of this approach, known as the Lucas Critique in economics literature, is that it usually cannot capture the first effect of policy changes on timber supply. This paper presents a new approach to estimate the timber supply function by introducing two applications in counterfactual comparisons. The approach seeks to optimize the supply function parameters under a given set of policy conditions. In the first application, we determine the change in the supply function following a change of the market regime and measure the welfare gain from competition in the timber market. The second application examines the effects of tree improvements on the timber supply function and on the producer and consumer surplus. These two cases illustrate that our approach is capable of determining the change in the supply function coefficients induced by policy or technological changes. Results from the second application also show that ignoring the change in supply functions leads to significant underestimate of the welfare effects of biotechnological improvements in forestry.

Numerical analysis of linear [formula omitted]-methods with two-layer boundary conditions for age-structured population models

Discrete age-structured population model with age dependent harvesting and its stability analysis

Using new survey data from Mexico, a dynamic econometric model is estimated to test the effect of policy changes on the flow of migrant labor from rural Mexico to the United States and test for differential effects of policy changes on male and female migration. We find that both IRCA and NAFTA reduced the share of rural Mexicans working in the United States. Increased U.S. border enforcement had the opposite effect. The impacts of these policy variables are small compared with those of macroeconomic variables. The influence of policy and macroeconomic variables is small compared with that of migration networks, as reflected in past migration by villagers to the United States. The effects of all of these variables on migration propensities differ, quantitatively and in some cases qualitatively, by gender.

Age-structured epidemic models are based on age-structured population models. Typically the linear age-structured population model, called the Lotka-McKendrick model, is used as a baseline population model in epidemic systems.

Population Dynamics: Mathematic Models of Population, Development, and Natural Resources

Environmental temperature is an important driver of the population dynamics of tsetse (Glossina spp) because the fly's immature stages are particularly vulnerable to temperatures (T) outside the range T = 16-32°C. Laboratory experiments carried out 50 years ago provide extensive measures of temperature-dependent rates of development, fat consumption and mortality in tsetse pupae. We improve on the models originally fitted to these data, providing better parameter estimates for use in population modelling. A composite function accurately models rates of pupal development for T = 8-32°C. Pupal duration can be estimated by summing the temperature-dependent daily percentage of development completed. Fat consumption is modelled as a logistic function of temperature; the total fat consumed during pupal development takes a minimum for T ≈ 25°C. Pupae experiencing constant temperatures <16°C exhaust their fat reserves before they complete development. At high temperatures, direct effects kill the pupae before fat stores are exhausted. The relationship between pupal mortality and temperature is well described by the sum of two exponential functions. Summing daily mortality rates over the whole pupal period does not reliably predict overall mortality. Mortality is more strongly correlated with the mean temperature experienced over pupal life or, for T ≤ 30°C, the fat consumption during this period. The new results will be particularly useful in the construction of various models for tsetse population dynamics, and will have particular relevance for agent-based models where the lives of individual tsetse are simulated using a daily time step.

Persistence in discrete age-structured population models

Asymptotic stability of delayed consumer age-structured population models with an Allee effect